An Assessment of macro-scalein situRaman and ultraviolet-induced fluorescence spectroscopy for rapid characterization of frozen peat and ground ice

Abstract

The search for life on other planets is an active area of research. Many of the likeliest planetary bodies, such as Europa, Enceladus, and Mars are characterized by cold surface environments and ice-rich terrains. Both Raman and ultraviolet-induced fluorescence (UIF) spectroscopies have been proposed as promising tools for the detection of various kinds of bioindicators in these environments. We examined whether macro-scale Raman and UIF spectroscopy could be applied to the analysis of unprocessed terrestrial frozen peat and clear ground ice samples for detection of bioindicators. It was found that this approach did not provide unambiguous detection of bioindicators, likely for a number of reasons, particularly due to strong broadband induced fluorescence. Other contributing factors may include degradation of organic matter in frozen peat to the point that compound-specific emitted fluorescence or Raman peaks were not resolvable. Our study does not downgrade the utility of either UIF or Raman spectroscopy for astrobiological investigations (which has been demonstrated in previous studies), but does suggest that the choice of instrumentation, operational conditions and sample preparation are important factors in ensuring the success of these techniques.

Biosignature detection by Mars rover equivalent instruments in samples from the CanMars Mars Sample Return Analogue Deployment

“…This is increasingly important as upcoming missions are focused on the search for past and present like (e.g., Mars 2020, EcoMars) where the primary objective is the direct detection of biosignatures, with organic molecules being an important target (Grotzinger, 2014;Domagal-Goldman and Wright, 2016;Rull et al, 2017). This objective has driven the development of a number of new flight instruments with analytical capabilities for the detection of organic molecules by LIBS and Raman (e.g, SuperCam, SHERLOC, RSL) (Jessberger et al, 2003;Skulinova et al, 2014;Eshelman et al, 2015;Dequaire et al, 2016;Laing et al, 2016.;Rull et al, 2017). While our LIBS experimental setup was not optimized for C detection, the detection limits for C in samples with <0.5% organic carbon have not been well established (Dequaire et al, 2016), so it is unlikely that LIBS data could have provided definitive C detection in most or any of the rover track samples.…”

“…The Raman measurements (532 nm, TR, UV) collected on the Hanksville samples all detected organic carbon with variable success in multiple samples. While the Hanksville samples all have TOC values of <0.07% with most below 0.03%, Raman spectroscopy has emerged as a powerful technique for the characterization and detection of low concentration organic compounds (Mars2020 SuperCam and SHERLOC, ExoMars RLS) (e.g., Skulinova et al, 2014;Cloutis et al, 2016, Ehlmann andEdwards, 2014;Eshelman et al, 2015;Laing et al, 2016;Abbey et al, 2017). The detection of~0.04 wt % condensed carbon has been reported in simulate Martian regolith samples by UV-Raman (Abbey et al, 2017), and Raman spectroscopy is capable of distinguishing between PAH compounds (Cloutis et al, 2016).…”